This invention relates generally to energy storage for the load leveling of power plants, and more particularly to load leveling storage schemes which simultaneously reduce the rate of peak heat rejection of an associated power plant.
The demand for electricity from a power system typically varies between a given base load and a higher peak rate. To accommodate this varying demand electrical power systems have historically operated their most efficient power plants in a constant "base loaded" mode and have added additional power plants to the system power grid as demand increases in order of decreasing power plant efficiency, with the least efficient plant being the last added.
More recently, load leveling systems involving the storage of energy have been introduced as a means of avoiding the use of less efficient power plants during periods of peak power demand, as well as to allow existing power plants to operate in the efficient "base loaded" mode while avoiding the addition of costly new peaking power plants. These load leveling systems typically involve the storage of energy (mechanical, electrical or thermal) in some reservoir during off-peak hours and withdrawing it during hours of greater need. The scarcity of suitable sites for pumped hydro-storage schemes and the projected high cost of electrical storage has resulted in a growing interest in thermal storage.
Conventional thermal storage systems include steam storage, hot water storage, and thermal storage in hot oil reservoirs. However, each of these conventional thermal storage systems requires that the stored thermal energy be withdrawn and converted to a useable form of energy during periods of peak power demand, thereby resulting in an increase in the peak heat rejection rate of the associated power plant.
The accommodation of this increased rate of peak heat rejection typically requires the construction and use of additional plant capacity to transfer the rejected heat to a heat sink. This additional capacity may be in the form of larger cooling towers, spray ponds, or the like. As a result, power plant construction, operating and maintenance costs are all significantly increased in power plants utilizing conventional thermal storage systems.
Accordingly, it is an object of the present invention to provide a new and improved method and system for increasing the deliverable peak power of a power plant while simultaneously reducing the rate of heat rejection typically associated with peak power production.
Thus, through the practice of the present invention a power plant intended to meet a given peak load can be designed with a primary power cycle having an output below the intended plant peak power output. Similarly, such a plant could include a rejected heat transfer capacity less than that required for a typical power plant of equal design peak power output, especially if compared to a power plant employing a conventional thermal storage system. Accordingly, the savings in capitol costs as well as in operating and maintenance costs resulting from the practice of the present invention are significant. Of course, it is appreciated that these benefits are not limited to electrical power systems, and that similar savings are obtainable with other power plants operating to satisfy variable power demands.